1. Field of the Invention
The present invention relates to an image generating apparatus that generates an image of a plurality of objects existing in a virtual three-dimensional space and the like, and more particularly, to generating an image in which a contour line is drawn in a target object among the plurality of objects.
2. Description of the Related Art
In video games, owing to recent improvement of process capabilities of video game devices, very realistic images can be drawn in three-dimensional computer graphics. However, in a game having a specific content, when the image is too realistic, the fun of the game decreases. Accordingly, in such a case, images of a cartoon style or an animation style are drawn in the three-dimensional computer graphics by using a technique called tuned rendering. A contour line is drawn in the contour of an object (hereinafter, referred to as a tuned object) for which a tuned rendering process is performed.
Here, when the thickness of the added contour line is too small, compared to the size of the tuned object, the contour line is not visually distinguished on the whole, and accordingly, representation of tune is deteriorated. On the other hand, when the thickness of the added contour line is too large, compared to the size of the tuned object, only the two-dimensional contour line is visually distinguished, and thereby representation of three-dimensional computer graphics is deteriorated. Accordingly, generally, it is configured that a thick contour line is set for a large tuned object and a thin contour line is set for a small tuned object.
Here, in a case where there is a plurality of tuned objects having different sizes, when distances to the tuned objects from a viewing point are approximately the same, a considerably desirable image is drawn. However, it cannot be determined that a plurality of objects is located in positions having approximately the same distance from the viewing point. For example, when a large tuned object is located in a position far from the viewing point and a small tuned object is located in a position close to the viewing point, there is a case that a contour line of a tuned object projected small is visually distinguished and a contour line of an object projected large is not visually distinguished, in an image that is generated by a perspective transformation process and is displayed on a screen.
In addition, even in a case where there is only one tuned object, when the distance from the viewing point changes, the size of the object in the image that is generated by the perspective transformation process and displayed on the screen changes. Accordingly, when the thickness of the contour line of the object is fixed, there is a case that a viewing person acquires a feeling of strangeness. Thus, in order to solve the above-described problems, technology in which the color and translucency of the contour line are configured to change in accordance with the distance from the viewing point and the size of the object after the perspective transformation process has been proposed (for example, see JP-A-2002-63581 (paragraphs 0070 to 0097).
However, in the technology disclosed in JP-A-2002-63581, when the distance from the viewing point to the tuned object exceeds a threshold value, the contour line of the tuned object becomes almost invisible. Accordingly, when the tuned object does not come near the viewing point to some degree, it cannot be known whether the tuned representation is made for a generated image. In addition, in a game or the like in which a tuned object and a non-tuned object are determined based on the properties of the objects, there is a case that a player mistakenly views an object as the tuned object or the non-tuned object and cannot perform an appropriate game operation.